Cannabinoid conversion in cannabis extracts

ABSTRACT

The present invention is a process for producing various types of  cannabis  extract from harvested  cannabis . A quantity of harvested  cannabis , which typically includes the inflorescence, floral leaves, and small stems of a flowering  cannabis  plants, is pre-frozen. The harvested  cannabis  is first subjected to cryogenic grinding to produce pulverized  cannabis . The pulverized  cannabis  is then subjected to alcohol extraction to produce an initial  cannabis  extract, which can be subjected to one of several forms of further processing according to the desired chemical profile of the final product. The initial  cannabis  extract may then be subjected to chemical processing that promote the conversion of THCA to Δ9 THC; the conversion of THCVA to THCV; the conversion of THCA to cannabinol (“CBN”); or the conversion of THCA to Δ8-THC.

This application is a continuation of U.S. patent application Ser. No.16/365,614, entitled “Producing Cannabis Extracts via SelectiveDecarboxylation” filed on Mar. 26, 2019, now U.S. Pat. No. 10,471,113,issued Nov. 12, 2019, which is incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

The cannabis plant (Cannabis sativa L.) (“cannabis”) has a long historyof being used for medicinal and recreational purposes. Cannabis plantmaterial contains a variety of chemical compounds, including thoseresponsible for the “high” associated with cannabis consumption as wellas other physiological effects. Among the compounds present in cannabisare tetrahydrocannabinolic acid (“THCA”) and tetrahydrocannabivaric acid(“THCVA”). While THCA and THCVA themselves produce few physiologicaleffects when directly ingested, exposing THCA and THCVA to hightemperatures, such as those produced when cannabis burns during smoking,causes those compounds to undergo decarboxylation reactions to formpsychoactive or other physiologically active compounds. THCA, inparticular, is well-known for its conversion via decarboxylation toΔ9-tetrahydrocannabinol (“Δ9-THC”), which is psychoactive. Upon heating,THCVA undergoes a similar decarboxylation reaction to formtetrahydrocannabivarin (“THCV”), which has appetite-suppressing effects.

As of February 2019, ten U.S. states have legalized the recreational useof cannabis, and thirty-two U.S. states have legalized the use ofcannabis for medicinal purposes. As the state-level legalization ofcannabis has expanded, so has the production of cannabis-derivedproducts. Cannabis extracts (sometimes known as “cannabis oils”) haveemerged as an important category of cannabis-derived product. Cannabisextracts are produced by subjecting cannabis to an extraction process,wherein solvents are used to dissolve (“extract”) chemical compoundsfrom harvested cannabis plant material.

In existing methods of making cannabis extracts, harvested cannabis orcannabis extract may be heated in an oven to achieve the decarboxylationof compounds, such as THCA and THCVA, to form psychoactive orphysiologically active compounds, such as Δ9-THC and THCV. A majordrawback of oven-based decarboxylation is the tendency to cause the lossof desirable volatile compounds, such as caryophyllene and otherterpenes, through evaporation or heat-induced chemical reactions.Accordingly, a process is needed to enable a greater degree of controlover the decarboxylation of cannabis extracts.

SUMMARY OF THE INVENTION

The present invention is a process for producing various types ofcannabis extract from harvested cannabis. A quantity of harvestedcannabis, which typically includes the inflorescence, floral leaves, andsmall stems of a flowering cannabis plants, is pre-frozen. The harvestedcannabis is first subjected to cryogenic grinding to produce pulverizedcannabis. The pulverized cannabis is then subjected to alcoholextraction to produce an initial cannabis extract, which can besubjected to one of several forms of further processing according to thedesired chemical profile of the final product. The initial cannabisextract may then be subjected to chemical processing that promote theconversion of THCA to Δ9-THC; the conversion of THCVA to THCV; theconversion of THCA to cannabinol (“CBN”); or the conversion of THCA toΔ8-tetrahydrocannabinol (“Δ8-THC”).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing the steps for converting harvestedcannabis to pulverized cannabis through cryogenic grinding;

FIG. 2 is a flow diagram showing the steps for converting pulverizedcannabis to an initial cannabis extract using alcohol extraction;

FIG. 3 is a flow diagram showing the steps for producing Δ9-THC and THCVvia decarboxylation of an initial cannabis extract;

FIG. 4 is a flow diagram showing the steps for producing cannabinol viadecarboxylation of an initial cannabis extract; and

FIG. 5 is a flow diagram showing the steps for producing Δ8-THC viadecarboxylation of a cannabis extract containing Δ9-THC.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a process that includes several stages, whichare described below as Stages 1-2, 3A-3C, and 4. Where the processrefers to the use of “alcohol,” a solution containing at least 99%ethanol by volume or at least 99% isopropyl alcohol by volume ispreferred although concentrations as low as about 95% alcohol can beused Specifically, “ethyl alcohol 200 proof” or “99.9% isopropylalcohol” supplied by Green Wood Cleaning Products, Inc., of Hollister,Calif., may be used.

Stage 1: Cryogenic Grinding

Referring to FIG. 1, cryogenic grinding is used to convert a quantity ofharvested cannabis 10 into pulverized cannabis 14. The harvestedcannabis 10, which may be fresh or cured, should be pre-frozen (step 11)at a temperature of about −29° C. (−20° F.) prior to processing.Cryogenic grinding should take place at an ambient temperature of 0-10°C. (32-50° F.). An ambient temperature of 0° C. (32° F.) is preferablefor minimizing the loss of compounds from the harvested cannabis throughevaporation or chemical reactions that would occur at highertemperatures, but acceptable results can still be obtained when theambient temperature is as high as 10° C. (50° F.). In practice, it isadvisable to perform cryogenic grinding in a cold room or a walk-infreezer.

When pre-freezing is complete, the harvested cannabis is separated intobatches (step 12) weighing approximately 450 g (1.0 lb) each. For eachbatch, the harvested cannabis is placed into a plastic bag capable ofaccommodating a volume of approximately 15 cm×48 cm×20 cm (6 in.×19in.×8 in.). A Reynolds® turkey-size oven cooking bag may be used. Thebag is then sealed; sealing may be accomplished by tying the open end ofthe bag into a knot or with a suitable fastener, such as twist tie. Thebatches of harvested cannabis are then processed in a tumbling apparatus(step 13).

The tumbling apparatus is a horizontally oriented cylindrical drum thatis capable of rotating about its own axis. The drum should be capable ofperforming approximately 40 rotations per minute (rpm). The drum mayhave a diameter of approximately 60 cm (24 in.) and a length ofapproximately 91 cm (36 in.). A Triminator® Dry cannabis-trimmingmachine supplied by Dana Mosman of Boulder, Colo., may serve as thetumbling apparatus.

Five bags of harvested cannabis are placed into the tumbling apparatus.Approximately 680 g (1.5 lb) of dry ice (i.e., solid carbon dioxide) isplaced into the tumbling apparatus along with the bags of harvestedcannabis. The dry ice may be in the form of uniformly sized cylindricalpieces that are approximately 0.64 cm (0.25 in.) in diameter andapproximately 5.0 cm (2.0 in) in height. Dry-ice “nuggets” supplied byPraxair Technology, Inc., of Danbury, Conn., may be used.

The bags of harvested cannabis are tumbled at approximately 40 rpm forabout 10 minutes. The appropriate rotational speed can be achieved witha Triminator® Dry cannabis-trimming machine or with a rheostatcontrolling the motor speed of a dedicated tumbler. During the tumblingprocess, the agitation of the harvested cannabis within each bag, inconjunction with the physical impacts of the dry ice against the bag,pulverize the harvested cannabis to a fine powder, thereby producingpulverized cannabis 14.

It will be appreciated that the amount of cannabis that can be processedby the tumbling apparatus depends on the size of the tumbling apparatus.The equipment can readily be scaled up for larger amounts of cannabis.

Stage 2: Alcohol Extraction

Referring to FIG. 2, alcohol extraction is used to separate thecompounds present within the pulverized cannabis from solid plantmatter. In preparation for alcohol extraction, the bags of pulverizedcannabis 14 are removed from the tumbling apparatus and transferred intofilter bags (step 21). Each batch of cannabis is transferred from theplastic bag used during cryogenic grinding to a filter bag having a porediameter of about 220 μm. The filter bag should be sufficiently large toaccommodate the pulverized cannabis without deliberate packing. A BubbleBags® filter bag with a nominal capacity of 3.78 L (1 gal) and a porediameter of 220 μm supplied by Fresh Headies Internet Sales Ltd. ofVancouver, Canada, may be used. Transfer of the pulverized cannabis ispreferably performed at the same ambient temperature as cryogenicgrinding to prevent premature warming of the pulverized cannabis.

Two filter-bags of pulverized cannabis are placed into an extractionapparatus for alcohol extraction (step 22). The extraction apparatus isan upright cylindrical drum that is capable of rotating about its ownaxis. The drum can have a diameter of approximately 38 cm (15 in.) andheight of approximately 38 cm (15 in.) and should be capable rotating at40 rpm. The extraction apparatus is prefilled with approximately 40 L(10 gal) of alcohol. The alcohol should completely immerse the filterbags without a risk of overflowing from the extraction apparatus. Thealcohol is preferably pre-chilled to −20° C. to −30° C., preferably to−25° C., to minimize any undesirable extraction of chlorophyll and lipidmaterial from the pulverized cannabis. The extraction process, however,will produce acceptable results with an alcohol temperature as high as0° C. (32° F.). To maintain chilling of the alcohol during theextraction process, the extraction apparatus may be placed in a chestfreezer or cold room.

Once immersed, the drum of the extraction apparatus is rotated atapproximately 40 rpm for 10 minutes, during which compounds from thepulverized cannabis dissolve into the alcohol. The alcohol normallytakes on a bright-green color as extraction proceeds. The alcohol isthen poured from the extraction apparatus for collection (step 23). Thefilter bags, which remain in the extraction apparatus, are subjected tocentrifugation at 200 g to spin out any residual alcohol that remainswithin the filter bags (step 24). The filter bags may be manuallyrearranged within the extraction apparatus prior to centrifugation toensure adequate balance. The residual alcohol is combined with thealcohol obtained by pouring.

The alcohol is then passed through a stainless-steel mesh filter with apore diameter of about 32 μm (step 25), and the filtrate (the“first-pass filtrate”) is collected. The first-pass filtrate is againpassed through the same filter (step 26), and the resultingtwice-filtered liquid (the “second-pass filtrate”) is collected. An8-inch diameter test sieve with a pore opening size of 32 μm (No. 450)supplied by W.S. Tyler (a division of Haver Tyler, Inc.) of Mentor,Ohio, may be used as the filter. The second-stage filtrate is subjectedto rotary evaporation at about 40° C. (104° F.) at a reduced pressure ofabout 5332 Pa (40 Torr or 0.05 atm) until substantially all of thealcohol is removed (step 27). The liquid that remains is the initialcannabis extract 28, which may be stored or subjected to one of thefurther processing steps designated as Stages 3A-3C below. For every twofilter-bags of pulverized cannabis, the extraction process producesapproximately 300 ml of initial cannabis extract. The initial cannabisextract is preferably stored at 0° C. (32° F.) while awaiting furtherprocessing.

A CUP-30 Centrifuge Utility Platform Alcohol Extraction System (the“CUP-30 system”) made by Delta Separations LLC of Santa Rosa, Calif.,may serve as the extraction apparatus. The ratio of alcohol topulverized cannabis described above (i.e., approximately 40 L of alcoholfor every 2 filter-bags of pulverized cannabis) may be scaled up tofully use the processing capacity of the CUP-30 system.

Stage 3A: Conversion of Tetrahydrocannabinolic Acid in the InitialCannabis Extract to Delta-9-Tetrahydrocannabinol

Referring to FIG. 3, a first diluted solution 31 is produced by dilutingthe initial cannabis extract 28 to 120% of its initial volume usingalcohol. For example, 80 ml of initial cannabis extract 28 should becombined with enough alcohol to produce 100 ml of the first dilutedsolution. The volume of the first diluted solution is further increasedby 3%-5% through the addition of water to produce a second dilutedsolution (step 32). For example, 100 ml of the first diluted solutionmay be combined with enough water to make 103-105 ml of the seconddiluted solution. The presence of the water within the second dilutedsolution inhibits the undesirable formation of cannabinol (“CBN”) aswell as the degradation of terpenes and cannabinoids.

The second diluted solution is refluxed at 80-100° C. for 1-3 hours,preferably 80° C. for 2 hours, to promote the decarboxylation of THCA toform Δ9-THC (step 33). Acceptable results can be obtained by refluxingat 100° C. for 1 hour, and the higher temperature may result in anincrease in the undesirable formation of CBN. Refluxing is performed ina flask attached to a cold condenser whose temperature is −30° C. to−40° C., preferably −40° C. The cold condenser may be cooled bypropylene glycol circulated by an external chiller. Following refluxing,the second diluted solution is subjected to rotary evaporation (step 35)until substantially all of the diluent is removed. The liquid thatremains is a refined cannabis extract enriched in Δ9-THC 36.

Refluxing may be used to process the initial cannabis extract in batchesof 300 ml. Batch sizes may be adjusted according to the capacity of therefluxing apparatus.

Stage 3B: Conversion of Tetrahydrocannabivaric Acid in the InitialCannabis Extract to Tetrahydrocannabivarin

Referring to FIG. 3, the initial cannabis extract 28 is converted to afirst diluted solution and then a second diluted solution (steps 31 and32) as in Stage 3A above. The second diluted solution is refluxed for1-2 hours, preferably 1.5 hours, at a temperature of 120° C. to promotethe decarboxylation of THCVA to form THCV (step 34). Refluxing isperformed in a flask attached to a cold condenser whose temperature is−30° C. to −40° C. The cold condenser may be chilled as in Stage 3Aabove. Following refluxing, the second diluted solution is subjected torotary evaporation (step 35) until substantially all diluent is removed.The liquid that remains is a refined cannabis extract that is enrichedin THCV 37.

Stage 3C: Increasing Cannabinol Content of Initial Cannabis Extract

Referring to FIG. 4, the initial cannabis extract 28 is diluted withalcohol to a concentration of 80% by volume to produce a dilutedsolution 41. For example, 80 ml of initial cannabis extract 28 should becombined with enough alcohol to produce 100 ml of the diluted solution.The diluted solution is refluxed at 180° C. for 1-3 hours, preferably 2hours, to promote the formation of cannabinol (step 42). Followingrefluxing, the diluted solution is subjected to rotary evaporation (step43) until substantially all alcohol is removed. The liquid that remainsis a refined cannabis extract that is enriched in cannabinol 44.

Stage 4: Increasing Δ8-Tetrahydrocannabinol Content of the InitialCannabis Extract

Referring to FIG. 4, the initial cannabis extract 28 is converted to arefined cannabis extract enriched in Δ9-THC 36 according to the steps inStage 3A above.

Referring to FIG. 5, the volume of the refined cannabis extract 36 isthen increased by 7.5%-15%, preferably 10%, by the addition of powderedbleaching clay (step 51). T-41 Canna Bleach supplied by Carbon ChemistryLtd. of Watkins, Colo., may be used. The volume of refined cannabisextract is then increased by another 7.5%-15%, preferably 10%, by theaddition of activated charcoal in powdered form (step 52). The volume ofpowdered bleaching clay added should be identical to the volume ofactivated charcoal added. Carbon Powder A supplied by Summit Research ofScotts Valley, Calif., may be used. For example, 100 ml of refinedcannabis extract may be combined with 7.5 cm³ of specialty bleachingclay and 7.5 cm³ of activated charcoal to produce a mixture having afinal volume of 115 ml.

The resulting mixture is subjected to distillation using a short-pathdistillation apparatus (the “distillation apparatus”). The distillationapparatus is composed of a feed flask, which contains the mixture. Thefeed flask is placed on a combination hotplate-magnetic stirrer, whichallows a liquid within the feed flask to be simultaneously heated andagitated by a stir bar. The feed flask is attached to a condenser,which, in turn, is preferably attached to a “triple cow”-styledistillation receiver with a connection point for a vacuum source. Twoflasks are connected to the distillation receiver, the first forcollecting undesirable distillates (the “waste flask”); and the secondfor collecting desirable distillates (the “collection flask”). Unneededconnections on the distillation apparatus should be sealed withstoppers. The temperature of the condenser is maintained at 21-23° C.(70-74° F.) by the circulation of water. A distillation receiver (Mfr.No. CG-1276-01) supplied by Thomas Scientific LLC of Swedesboro, N.J.,may be used.

The mixture is placed into the feed flask, and the waste flask is placedin a position to receive distillate. The distillation apparatus isconnected to a vacuum source, and the pressure within the distillationapparatus is reduced to approximately 66.7 Pa (500 mTorr or 6.7×10⁻⁴atm). The mixture is gradually heated to 140° C. while being agitated bythe stir bar (step 53). It is important to ensure that the mixture doesnot foam (or “muffin”) during distillation. Uncontrolled foam may expandto reach and contaminate the condenser, making the distillate unsuitablefor use. To minimize foaming, it is advisable to set the stir bar to aninitial speed of 400 rpm. The mixture is then gradually heated at a rateof approximately 15° C. per minute, and speed of the stir bar increasedat a rate of approximately 50 rpm per minute, until the mixture reaches140° C. and the stir bar reaches 900 rpm. Any distillate thatincidentally emerges during the initial heating process is collected inthe waste flask.

Once the mixture reaches 140° C., the distillate should take on a bluishcolor as azulene and derivatives thereof begin to distill from themixture. Heating of the mixture should continue at the rate ofapproximately 1° C. per minute until the mixture reaches 157° C. Duringthe heating period, bluish distillate continues to distill from themixture and is collected in the waste flask (step 54). The temperatureof the mixture is maintained at 157° C. until the condensing distillateis colorless, at which point all azulene and derivatives thereof havebeen removed from the mixture.

The colorless distillate is collected in the collection flask, whichshould be rotated into position as soon as bluish distillate stopsappearing. The temperature of the mixture is further increased at therate of approximately 1° C. per minute until it reaches 175° C. Thedistillate, which now contains Δ8-THC, continues to be collected in thecollection flask during this period (step 55). The mixture is maintainedat a temperature of 175° C. until substantially all of the liquid in thefeed flask is depleted. The mixture is then heated to 220° C., anddistillate is collected until no further distillate is produced (step56). The final heating to 220° C. promotes the full conversion of liquidremaining in the feed flask to the vapor phase. The distillate is arefined cannabis extract enriched in Δ8-THC 57.

The refined cannabis extract enriched in Δ8-THC 57 should be colorless.If the distillate in the collection flask has a noticeable color, suchas amber or teal, the distillate should be treated as the cannabisextract enriched in Δ9-THC 36 and subjected to a second round ofprocessing according to steps 51-56.

Referring to FIG. 4, the initial cannabis extract 28 is diluted withalcohol to a concentration of 90% by volume to produce a dilutedsolution 41. For example, 90 ml of initial cannabis extract 30 should becombined with enough alcohol to produce 100 ml of the diluted solution.The magnetic stirrer is turned on to about 500 rpm. The diluted solutionis then refluxed at between 180° C.-220° C. for 1-3 hours, preferably 2hours, to promote the formation of cannabinol (step 42). Followingrefluxing, the diluted solution is subjected to rotary evaporation (step43) until substantially all alcohol is removed. The liquid that remainsis a refined cannabis extract that is enriched in cannabinol 44.

Referring to FIG. 4, the initial cannabis extract 28 is converted to arefined cannabis extract enriched in CBN 44 according to the steps inStage 3C above.

The following claims are thus to be understood to include what isspecifically illustrated and described above; what is conceptuallyequivalent; and what can be obviously substituted. Those skilled in theart will appreciate that various adaptations and modifications of thejust-described preferred embodiment can be configured without departingfrom the scope of the invention. The illustrated embodiment has been setforth only for the purposes of example and should not be taken aslimiting the invention. Therefore, it is to be understood that, withinthe scope of the appended claims, the invention may be practiced otherthan as specifically described herein.

What is claimed is:
 1. A method of decarboxylating a cannabis extractconsisting essentially of: adding a quantity of ethanol to an initialcannabis extract to produce a first diluted solution; adding a quantityof water to the first diluted solution to produce a second dilutedsolution; and refluxing the second diluted solution at a temperature ofabout 80° C.-120° C. for a period of about 1-3 hours; after refluxing,adding a quantity of bleaching clay and a quantity of activated charcoalto the second diluted solution to produce a mixture; and distilling themixture at a temperature of about 157° C.-220° C. to produce thedecarboxylated cannabis extract.